Process of forming dental restoration.



n. w. swmmm. PROCESS OF FORMING DENTAL RESTORATION.

APPLICATION FILED 05c. 1e, 1913.

Patented Oct. 23,1917.

2 SHEETS-SHEET 1 INV ENTOR.

'WITNEISSDESI R. W. SWEETNAM.

PROCESS OF FORMING DENTAL RESTORATION.

APPLICATION FILED 0mm. ms.

Patented 00. 23, 1917.

2 SHEETS-SHEET 2 WITNESSESZ lNVE-NTOR.

- UNITED STATES PATENT OFFICE.

ROBERT W. SWEETNAM, OF TOLEDO, OHIO.

"the cavity with molten fluid or molded or plastic material. Points areselected accordthe metal maybe drawn to or -minutest recesses and mostremote parts PROCESS OF FORMING- DENTAL RESTORATION.

To all whom it may concern: 1

Be it known that I, ROBERT W. Swear- NAM, a citizen of the UnitedStates, and a resident of Toledo, in the countyof Lucas and State ofOhio, have invented a certain new and useful Process of Forming DentalRestoration; and I do hereby declare the following to be a full, clear,and exact description of the invention, such as .will enable othersskilled in the art to which it appertains to make and use the same,reference being had to the accompan ing drawings, and to the characters0 reference marked thereon, which form a part of this specification.

My invention relates to processes of forming dental restorations, .suchas inlays, bridges, plates, etc. It particularly has for its object toproduce castings that for allpractical purposes conformperfectly withthe configuration to be restored.

By my invention, air is removed from and drawn toward or directed to oneor more points located in the vicinity of the molded cavity, before,during, or after the filling of ing to the shape of the castings to bemade,

according to the way the metal should be cooled in its several parts,according to the way the metal should be first placed and held while thecavity is "being filled in order that forced into the in the moldedcavity, or cooled, or pressed,

or forced to shape to prevent globular for-' mation, or in order thatthe metal may be cooled uniformly by the passing of the air to preventdistortion and warping or in order to enlarge the casting whichovercomes the effect of contraction. The outer edges and surface thusbecome sharp and defined and the castsolid throughout and practically areproduction of the pattern.

I shall describe hereinafter, processes in which the use of my inventionis involved and will illustrate in the drawings and describe certainapparatus usable in the conduct of my invention.

In the drawings Figure 1 illustrates a means for forming equalizingpassages in the mold. -Fig. 2 is an enlarged view of one of detailsshown in Fig. 1. Fig. 3 is a top view of the detail of constructionSpecification of Letters Patent. Patented 0013. 23, 191 '7. Applicationfiled December 18, 1913. Serial No. 807,453.

.shown in Fig. 2. .Fig. 4 is an angular perforated tube for formingequalizing passages. Fig. 5 shows the pattern mounted. Fig. 6, shows thecast completed and the manner in which the mold is treated. Fig. 7 showsan arrangement of patterns 1nount-' ed ready for molding. Fig. 8 showsthe cast of the pattern shown in Fig. 7 completed. Fig. 9 shows a methodof supporting the pattern and the material for forming equalizingpassages. Fig. 10 shows the connections and mounting completed. F'g. 11showsa further modification, wherein the pattern is coated. Fig. 12,shows the cast of the pattern of Fig. 11 completed. Fig. 13 shows amodification of the processes illustrated conventionally in Fig. 11.Fig. 14 isa modification of the equalizing device shown in Fig. 1. Fig.15 shows a modified method of supporting the material for formingequalizing passage. Fig. 16 illustrates a further. modification of thedevice shown in Fig. 15. Fig. 17 illustrates conventionally a method ofpermitting the air to press only upon the surface of the metal locatedon the outside of the metal. Fig. 18 illustrates a further modificationof the device shown in-Fig. 14.

1, in Fig. 1, is the device which I have termed the equalizer orregulator. 2 are adjustable rods which are adjustably supported withreference to a frame 3. The frame 3 may be located on an investment cupor flask, and the rods may be extended into the investment cup or flask.The rods are supported by cranes or brackets 4, which extend over theinterior ofthe cup. Their inner ends are provided with rings 5. In therings 5 are located hemispheres 6, which fit around the rods 2 andsocket in the rings 5. Each ring is provided with a small screw 7, whichpresses upon the hemispheres 6 to hold the rods in position. The screws7 may be unscrewed and the rods 2 may be shown in Fig. 4 may be insertedon the ends of the rods 2. The tube may be' bent to any desired shape.,The tube 10 may, be provided with a slit v11. The ends of the rods areinserted in the ends of the tubes so that when the rods 2 are withdrawnthey will leave the tubes 11 in theinvestment. The slit 11 and theopening end 12 is closed by disappearing materials, such as waxy mate'-rials, bef0re the flask is filled with an investment, material. When theflask s heated, after the investment material 1s suitably dried the,disappearing materlal used to cover the slit 11 and the opening 12 I Iwill be absorbed by the investment material or driven out through theopenings formed in the mold by withdrawal of the supporting rods 2. v

In the conduct of the processes involving my invention, the pattern 20formed of wax is supported upon a sprue wire 21, as shown in Fig. 5. Thespruewire 21 is supported upon the sprue-former 22. The sprueformer'22may be provided with an opening 23 filled with a wax-like material'whichis adaptedto receive the sprue wire 21. In order that the metal mayreach the extreme, smaller or finer points or parts of the matrix orcavity formed" by the pattern 20, by-passages may be formed in the moldleading from the sprue-hole to the extremities or finer or sharperpoints of the molded cavity. This is accomplished by connecting theedges or corners of the pattern 20 with the sprue-wire 20 with a stripof disappearing material 24.

The flask 30 is then placed over theisprue former 22. The equalizer 1,as shown in Fig. 1, is placed over the top of the flask 30 and the rods2 are so adjusted as to bring them in the vicinity of points from whenceit is desired to remove the air. The feet 8 are shaped and the rodsarelocated so as to bring their ends at the desired points relative tothe pattern 20 and so as to form passage ways in the mold along desiredparts of the pattern.

The investment cup 30 is then filled with the porous investment materialin a plastic condition. It fills in around the pattern 20, thedisappearing strips 24 and the rods 2, and their angular or sharpenedextremities 8 or around the split tubes 10 if they are material'has setand suitably dried, the rods 2 are withdrawn which leave the tips orpoints 8 of waxy material within the investment material or, if thetubes 10 are used in place of the tips 8, they will be left in theplaced on the rods 2. When the investment I investment material,togetherwith the disappearing material with which the openings of the tubes areplugged or covered. The flask is then subjected to heat and the waxpattern and thedisappearing'material in the moldare melted and finallyabsorbed by the investment material and if the heat is suflicientlygreat, it will be burnt out or driven off as a gas through .theopenings.

.This leaves passage ways in the mold around the matrix or moldedcavity. The mold thus formed is illustrated in Fig. 6.

The mold is then centrally seated upon a plate pneumatically connectedwith a system or apparatus having vacuum capacity. Metal is then placedover the sprue-hole and melted or molten metal is poured into thesprue-hole. It passes into the cavity formed by the pattern and throughthe by-passages leading to the extreme or other desired points of thematrix except so far as it may lee-prevented by the air contained in thecavity formed in the mold. The connection with the vacuum producingapparatus is then opened and the air is withdrawn from the'passag'es 34.The air'is thus drawnthrough the walls of the moldedcavity at pointswhere it is essential to remove the air; The metal will thus be held andallowed to form in a substantially uniform vacuous surrounding. Thevacuous condition will work out through the investment material from thepassages as well as work up from the bottom of the mold so as to drawthe air away from the pattern. In order to regulate the pressure broughtto bear upon the surface of the metal in the sprue-hole, the flask maybe covered or coated, and be placed under a compression cap 58 and airunder pressure may be directed in between the cap and the coating orcovering on the investment material in the flask which will press uponthe surface of the metal in the sprue-hole. This pressure will behydrostatically transmitted to the molten metal contained in the moldedcavity and the wall of the cavity will be pressed outward in alldirections. terial being more or less compressible and the air beingwithdrawn from the investment material contained in the flask andprincipally from the investment material surrounding the molded cavity,the cavity enlarges according to the pressure of the air directed uponthe surfaceof the molten metal in the sprue-hole. Expansibility' ofparts of the walls of the cavity, such as the inner wall, may bemodified with respect to the expansibility of the other parts of the Theinvestment mawall of the cavity by varying the thickness or distancebetween the mol ed. cavity and the air passage from which the air iswithdrawn or by directing air under pressure to parts in the vicinity ofparts of the wall of the cavity thus sustaining it such as directing.air under pressure into a cavity located within a .ring, as illustratedin Fig. 8. The passages extending'above and around the pattern atsubstantially all its outer or extreme points the molten metal will beequally pressed into the cavity\ and outward in all directions by theair pressing upon its sur face in the sprue of the'mold and transmitmitsthe metal to be pressed into the finest edges and corners'of the moldedcavity and held in position while it solidifies.-

The plate 31 is provided with a seat 35.

The interior portion 36 of theplate is depressed. The flask is providedwith an inturned portion 37 which coiiperates with the seat to make aperfect air tight connection. The mold being formed ofinvestmentmaterial which is more or less granular when dried, particlessometimes break off particularly from the trimmed end of the investmentcup and from-theedges of the cavity formed bywithdrawing the rods 2.

'The particles fall into the depression 36 is hot and pliab e and madesmaller than which is deep enough to avoid the formation of any spacebetween the lower edge of the flask and the seat 35 through which airwould pass. The plate 31 may be made for flasks of diflerent sizes byforming a wide annular seat 35. The smaller flasks may be centered byusing rings of different sizes.

The ring 38 may be inserted or placed on the plate 31 and the smallerflask 3O placed in the ring.

If it is desired, a casting may be distended by air pressure. This maybe done to overcome undue contraction or tomold the metal while hotand'moldable and make the casting conform to the size of the outersurface of the pattern or the metal itself may be molded b pressurewhile the metal the usual cast. The method of operation whereby thesethings may be accomplished is conventionally illustrated in Figs. 7 and8.

The sprue-former 22 may be provided with a plurality of sprue-wires 40which will hold the wax pattern 41 in position and will also form aplurality of passages leading from the sprue to the pattern. A see- 0ndpattern 42. is also supported on the sprue-former. This may be locatedcentrally with respect to the first pattern 41. The pattern 42-maybemade of a disappearing material. The patterns may be metallic,perforated hollow forms having the openings therein filled with wax. Thepattern 42 is located centrally with respectto the pattern 41 and issupported by wires 43.' The wires 43 are supported on the sprue-former22. The outer edge of the sprue-former 22 may be provided with a groove44 as shown in Figs. 7, 9 and 10 which may be filled with wax. Ifdesired, holes 45 may be formed in the sprue-former which extend to thegroove 44. The wires 43 ma be located at any point in the grove. 4 orthey may be located in the holes 45. When their .ends are surroundedwith wax in the groove 44 or in the holes 45 the rods 43 are held inposition.

The flask 50 is then placed over the sprueformer and the equalizer isplaced on the outeredge of the flask.

The flask 50 is then filled with a plastic investment material so thatit completelysurrounds the rods,- the patterns and strip of wax-likematerial. When the investment material has set and sufliciently dried,the rods 2 are withdrawn, the equalizer removed, the flask inverted, thesprue-former 22 removed and the wires 40 and 43 withdrawn The flask isthen heated until the disappearing material is melted and absorbed bythe investment material or is burnt ofl" or'driven off as a gas. It willhave the cavity 51 formed by the pattern 41 is connected to the centralparts of the sprue by means of the passages 55 formed by the wires 40while the cavity 53 is connected to the bottom of the flask by means ofthe passages .56 formed by the rods'2.

The flask. 50 is placed upon the vacuum plate 31 and the metal is meltedin the sprue ofvthe mold or molten metal is poured into the sprue. Themolten metal 57 passes down through the sprue-hole 55 to themoldedcavity 52 as the air is withdrawn from the vacuumwplate 31 byturning the stop-cock 33. The pressure of the air on the outer surfaceof the metal is transm'it ted through the passage ways 55 to the metalin the cavity 52 which presses the metal tightly against the outer wallofthe I cavity. The atmospheric air passes down through the passages 54and enters the cavity 51 so that the air presses uniformly outward fromthe cavity 51 against'the metal while in a moldable state and alsopasses to the cavity 53 whereby the metal inthe cavity 52 is drawn andforced outporous material in the cavity 51 to the cavity 53.

If't is desired, air under pressure may 4 be directed to the cavity 51through the air passages 54. This is accomplished by the means shown inFig. '8. The plate 58 having a packing ring 59 is placed over the upperedge of the flask 50. The plate is connected with a pipe 60 which may inturn be connected to' a pump or with an apparatus havin air underpressure. The air will then be orced down through the passages 54 andthe cavity 51 and against the metal. The metal in the cavity 52 while ina moldable state, will be forced outward and if the .air pressures in.the cavities are properly manipulated it may be forced to the outer walland shrinkage prevented.

In Figs. 9 and 10 is shown conventionally a method of surrounding amatrix with a spiral air passage.

The general shape of the air passage may thus be made to conform withthe shape of the molded cavity. Wires 62 are supported in the outer edgeof the sprue-former 39,

as in the trough 44' or in the holes 45 and secured in position by meansof wax. Theupper ends of the rods 62 are bent so as to conform to theshape of the pattern 20. A strip of disappearing materlal 63 is thenwound around the upper ends of the wires 62 forming thereby, after theflask has been heated, a circuitous passage around the pattern. The rods2. are then warmed slightly and brought in contact with the spiral strip63 and a temporary sealing connection is made therewith. When the flask30 is filled with the investment material and the sprueformer 39 andthe, sprue-wire 21 is withdrawn and the flask is heated the matrix andthe circuitous passageare formed. The flask 30 may then be placed uponthe-vacuum plate 31 and the air withdrawn. This will remove all of theair from around the molded cavity which will drive the metal outward tothe outer surface of the cavity in all directions to substantially thesame degree so that the metal is'received in a unlform low pressureenvironment.

paintingthe surface of the pattern 20 with,

or dipping the pattern'in'plasticinvestment material, forming therebyiaout 70 on the outer surface of the pattern 20 1f necessary, thepattern-,may be 'covered'several times with the investment material soas to thicken the coat 70. When thecoat has.

dried it may be covered with a coat of waxy material by dipping orotherwise.- If desired, the waxy. material 71 maybe mixed means? terialwhich will resist fire and form a binder or bridging points between thelayer of invest-- ment material 70- and'the surrounding investmentmaterial forming the mold. This will strengthen the wall or coat 70surrounding the cavity when the pattern 20 andthe disappearing materialof the coat 71 is withdrawn by heating the flask. The flask 30 may thenbe placed over the sprue-former 22 and the equalizer 1 placed on theupper end of the flask and the rods 2 brought into sealing contact withthe coat 71. The flask is then filledv with investment material.

When it has been sufiiciently dried, the rods metal may be melted in thesprue or poured in the sprue and the connection with the vacuum pumpmade, whereupon the metal will be drawn into all parts of the pattern byreason of the fact that the air is drawn from the cavity producing auniform vacuous condition around the cavity. Inasmuch as the coat 71contains asbestos fiber or a granular fire resisting material, the fiberorthe particles will remain in the cavity formed by melting thedisappearing material contained in the coat 71 and will form bridgingpoints between the surfaces of the cavit and will hold the wall formedby the coat 0 in osition in the flask 30 after the mold has en completedand will also prevent cracking by the heat of the metal. When the metalis melted or poured and'the air is withdrawn from the surrounding cavitthe metal will bedrawn outwardin all irections by the suction.

. As shown in Fi .13 the coat 70 may be wound by a strip 2 ofdisappearing material. It may be wound around the coat 70 and crossed inall directions.

of the strip. The pattern is then placed 111 This will leave smallspaces in between the windings vestment material after connection hasbeen made with the rods 2. The investment ma- .nection with the coat 70so that when the In Figs. 11, 12 and 13 is shown a further investmentmaterial-has been dried and the pattern 20 removed, and the disappearinmaterial of the strip 72 driven off, the wa penetrating betweenthewindings of the strips 72.

In Fig. 14 is shown a modification of the device shown in Fig. 1. In thedevice shown in Fig. 14, rods 2 are supported on the flask 80. The flask80 is provided with an inturned flange 81 and an annular collar 82. Theflange 81 and the collar 82 are wall of the flask 80 and bind againstthe hemispheres 84 so that'the rods 82 may be adjusted longitudinallyand an larly with respect to the interior of the ask and securelyclamped in position by the screws 85. The upper edge 86 of the collar82extends above the flange 81 and the hemispheres 84 in order toprovide" a seat for'the-flask 80 when it is placed upon the vacuum plate31.

In Fig. 15 is shown a modification of the means for supporting strips ofdisappearing material. The strip containing d sappearing material may bebent to any shape. If desired, it may be bent so as to spirally surroundthe pattern 20. It is supported by means of the ferrule 90 which may bemounted on the sprue-wire 21 at any desired point. It is provided with athimble 91 extending at right angles to the ferrule 90. The inner end ofthe thimble 91 is closed so as toprevent communication between thepassages produced by the sprue wire and the strip. The strip is insertedinto the thimble 91. The strip of disappearing material 92 may containor be wound with a strand of wire 7 150, which will hold it-in positionWhile the flask 30 is being filled with the plastic investment material.The strip 92 may be continued through to the bottom of the flask 30 orit may terminate in the vicinityof the bottom of the flask. Thesprue-former 22 is removed and the sprue wire 21 is withdrawn leavingthe ferrule 90 and the strip 92 in the mold. The flask isthen heated andthe disappearing material contained in the strip 92 is absorbed by theporous investment ma-.

te'rial. The pattern 20 also passes ofl as' a gas and is partiallyabsorbed by the investment material. If the strip 92, while in theprocess of formation of the mold, extends to the bottom forming aconnecting passage to the interior, the air will be withdrawn directlyfrom the passage surrounding the molded cavity. Or'if the end of thestr1p 92 extends only to the vicinity of the bottom of the flask 30 theair will be drawn from the lower part of the passage through the thinwall of the investment material formed between the lower part of thepassageand the vacuum plate 31. The molten metal will thus be drawn intoevery part of the molten cavity as above.

In Fig. 16 is shown a further modlfication of the device shown in Fig..15. In Fig; 16 a slitted tube 95 is supported on or secured to theferrule 90. The slit 96 and the opening 97 at the end of the tube 95 arefilled or .covered with a waxy material by d ppmg' in wax. The flask 30is filled w1th mvest- 123. The shell is provided with an inwardly willbe withdrawn from the shell and from ment material and heated. Pattern20 together with sealing material used to cover the openings of the tube95, will be driven out or absorbed .by the investment material containedin the flask. The tube may extend through the investment material 'ormerelyto a oint near the bottom as in the case of. they orm shown inFig. 15. In Fig. 17 is illustrated conventionally the process applied toa further modified form of equalizer. The mold is formed in aninvestment material located in a flask 120, havin openings121 and asealing flange 122. he flask 120 is supported in a shell extendingflange 124. The flange 122 of the flask 120 seats upon the flange 124.

When the mold is formed in the flask 120,

rods are inserted in the holes 121 located in the wall of .the flask 120and extend inwardly and toward the pattern to points in the vicinity ofthe extremities of the pat-" tern or to points near the surface of thepattern and are located with reference to the pattern so as to obtainthe results desired as heretofore explained. The flask 120 is filledwith investment material and the mold completed. The sprue former andthe sprue wire are withdrawn and the rods inserted in the holes of thewall of the flask are Withdrawn after the investment material is dried.The 'disappearing material of the pattern and any disappearing materialthat may be used in connection with the rods inserted in the walls ofthe flask 120 are driven off by heating the flask and the contentsandthe flask 120 is inserted in the, shell 123. The shell and flask isthen placed upon the vacuum plate 31 whereupon air points in thevicinity of the molded cavity through the passage ways formed by thewires previously inserted in the holes of the wall of the flask 120. Ifdesired, a compression cap like that shown in Fig. .8 may be placed onthe flange 122 and the airunder pressure directed upon the surface ofthe investment material contained in the flask or if the sprue of themold is covered with a non-porous coating or covering, the air pres- 115sure transmitted through the sprue hole may be made to afl'ect'the metalcontained within the molded cavity.

When the flask 30 is placed upon the vacuum plate 31, the air iswithdrawn from 120 the investment material contained in the flask andfrom the molded cavity, Whereupon the molten metal which completelycovers the opening formed in the non-porous coating will be forced downby the atmos- 125 pheric pressure into all parts of the cavity. The airpressure will thus be directly transmitted through the molten metalwhich will i be forced into all parts of the molded cavity.

In Fig. 18 is also shown a means for seal- 130; a

ing the surface of the sprue, so as to prevent the air from dissipatingitself and penetrating the'investment material contained in the flask orcup. The sprue former -consists of a conical shaped body of sheet metal.110. It is made so as to fit the large end of the flask 30. Near theouter edge of the sprue former an inwardly-extending ridge 111 islocated. A wafer of asbestos 112 suitably formed ma be inserted-in theunder side of the sprue ormer 110 and crowded beyond the inwardlyextending ridge 111. The wafer 112 will thus be held in position by theridge 111. The conical body 110 is provided with a central opening 113through which the sprue wire 21 may be inserted. The asbestos wafer isalso provided with the opening 115, which 31S adapted to register withthe opening 113. The inner edge of the wafer 112 about the opening 115extends beyond the inner edge of the conical body or sprue former 110.The under side of the sprue former is filled with wax 116. The wax 116aids in holding the asbestos wafer 112 in position and also penetrateswithin the ridges 111. The sprue wire 21 is inserted through theopenings 113 and 115 into the wax 116. The pattern 20 is supported onthe sprue wire. The flask 30 is placed over the sprue former 11 0 and isthen filled with investment material. -When the investment material, issuitably dried and hardened the flask is inverted and the wax 116 iswithdrawn. The investment material being in the nature of a cement theinner edges of the asbestos wafer 112 are securely cemented to thesurface of the porous matei rial surrounding the sprue holder, or theedge of the asbestos may be provided with a turned edge which will befilled with the cement and locked in position or it may be locked in anyother manner. After removal of the wax 116, the sprue wire 21 iswithdrawn. The flask is then heated which drives out all of the waxcontained in the pattern and that may be used for forming air passagesabout the pattern, which .is melted and either burnt off or driven outof the passages as a gas. The metal is then poured or melted and allowedto flow in through the sprue hole to the pattern, and sufiicient metalis used so that 1t will cover the inner edge of the asbestos wafer aboutthe opening 115. When the flask is placed upon the receiver-plate 31 andthe air is withdrawn from the cells of the investment material the airwill press at atmospheric pressure against the surface of the metal onthe outside of the mold and force the metal into every part of themolded cavity. The pressure will be transmitted through the metalcontained in the spruehole, and thus it will press the metal outward inevery direction. The asbestos wafer. 112, being sealed to the surface ofthe investment material around the edges of the opening 115, the

um will operate to remove all the air of the investment materialcontained in the cup. Moreover, the air will press upon the surface ofthe metal in the sprue hole and this pres-.

sure will be transmitted" through the metal I in the sprue hole'to themetal in the moldedcavity and force the metal into all parts of thecavity. If the flask 1s placed under a compression cap, the metal 1n thecavlty may be pressed outward in all directions by a pressure aboveatmospheric pressure. The

investment material being.more or less compressible, the cavity may beslightly enlarged sufficient to overcome the reduction in size pressedby. the contraction of the metal when cooling. The compressibility ofthe investment material may be modified by its composition and thepressure placed on the sur ace of the metal in the sprue hole may alsobe regulated so that the size or volume may be re ulated and so that thesize of the cast may e regulated to the same degree.

The process involving the use of my invention which I have described maybe further modified and may be used in connection with a great varietyof apparatuses and devices wlthout departing from the spirit of theinvention.

What I claim as new and desire to secureby Letters Patent is as follows:

1. The process of forming dental castings which consists in forming amold in a porous material and a bridged air space in the moldsurrounding the cavity directing molten 'metal into the molded cavityand removing the air from the space.

2. The process of formingcastings which consists in supporting a patternand a waxed strip in the vicinity of the patternand forming a mold aboutthe pattern and the wax strip and heating the mold to withdraw thepattern, and wax strip directing -molten metal into the molded cavityand removing the air from the space formed by the wax strip when themolded cavity is filled with molten metal.

3. The process of forming dental castings which consists in forming amold in a porous material and spaces in the porous material at points inthe vicinity of the molded cavity and supplying air to one of the spacesand removing the air from another one of the spaces.

4. The process of forming dental castings nus which consists in forminga mold in a porous I material, forming spaces in said mold at points inthe vicinity of the mold and directing air to the spaces.

which consists in forming a mold in a porous material, forming spaces insaid mold at points in the vicinity of the mold and supplying air underpressure to one of the spaces, and removing it from another of thespaces. y

6. The process of forming dental castings which consists in forming amold in a porous material and forming a space in said'mold conformingsubstantially to the contour of the molded cavity and supplying airunder pressure to the said space.

7 The process of forming dental castings which consists in forming amold in a porous 5. The process of forming dental castings.

-material and an air space conforming to the contour of the moldedcavity and on the outside of the cavity, and an air space conforming tothe contour of the interior surface of the cavity and removing the airfrom one of the said spaces and supplying air to the other. of the saidspaces.

8. The process of forming dental castings which consists in formingamold in a porous 1 material and an air space conforming, to

the contour of the molded cavity and on-the vicinity of the moldedcavity, directing airv under pressure to the surface of the molten metalto compress the materlal and Withdrawing air from the passages.

- 10. The process of forming dental castings Which consists in forming amold in a porous compressible mater al forming a passage 111 thevicinity of the molded cavity and direct-- ing air under pressure to thesurface of the metal while in the molten state to modify parts of thewall of the cavity.

In testimony whereof, I hereunto sign my name to this specification inthe presence of two subscribing witnesses.

ROBERT w. SWEETNAM.

Witnesses:

S. T. KLoTz, F. AUL.

